1. Field of the Invention
The present invention relates to an electrodynamic speaker that is preferably used in vehicles or the like, and in particular, to such a speaker that can be installed in a high-temperature environment such as an engine compartment.
2. Description of the Related Art
When a relatively large car speaker for reproducing sounds in a low-frequency range, such as a subwoofer, is installed in a vehicle cabin, the available space in the vehicle cabin is reduced. Therefore, in recent years, a method has been used in which a speaker is disposed in a space outside of a vehicle cabin, and reproduced sound generated by the speaker is emitted to a space inside of the vehicle cabin through an opening formed in a wall of the vehicle cabin. However, it may be difficult to form a large opening in a wall of a vehicle cabin so as to face the diaphragm of a speaker.
Technologies have been proposed with which a duct is formed so as to protrude from a case (cabinet), which is the enclosure of a speaker, and the duct is inserted into a hole formed in a wall of a vehicle cabin so that a space in the case, which is disposed outside of a vehicle cabin, communicates with a space in the vehicle cabin through the duct (see, for example, International Publication No. WO2011/047435). With such a speaker, reproduced sound generated in the case is emitted through a distal open end of the duct into a cabin space, which is an acoustic space. Therefore, the distal open end of the duct is a sound port.
When installing a speaker in an installation space outside of a vehicle cabin of an automobile, a space in a trunk or a space in a door is usually used as the installation space. An engine compartment also has a relatively large extra space in which a speaker can be installed. However, when a speaker is installed in a high-temperature environment such as an engine compartment, the temperature of a voice coil becomes excessively high. As a result, the voice coil may become loose, the neodymium (Nd) magnet used in a magnetic circuit may become demagnetized, or other faults may occur. Therefore, when installing a speaker in a high-temperature environment such as an engine compartment, it is necessary to take special measures to efficiently dissipate heat of the speaker.